The present invention relates to an apparatus and a method for measuring radiation emanating from a sample containing a radiant matter.
Certain conditions and diseases can be indicated by analysing a sample of exhaled air in order to establish the concentration of a certain substance. One example is a method of detecting Helicobacter Pylori in the gastro-intestinal tract, a good indication of gastric ulcer, by measuring in exhaled CO2 the concentration of 14C, used as a label for a urea preparation swallowed prior to the measurement. The concentration is determined by measuring xcex2-radiation emanating from 14C. However, since the emanation from 14C is low energy xcex2-radiation this method today requires the use of expensive, time consuming and bulky apparatus.
The provision of simple and cheap methods for use in decentralised health care has still not been adequately solved. Thus, there is a need for methods and improved apparatuses for detecting low energy radiation, particularly for use in health care, which are simple, cheap, small, and which provide satisfactory diagnostic accuracy.
An object of the present invention is to provide a method for measuring low energy radiation emanating from a radiant matter in a sample, particularly for measuring xcex2-radiation emanating from a 14C labelled compound, that is fast, simple and provides satisfactory accuracy.
A further object of the present invention is to provide an apparatus for measuring low energy radiation emanating from a radiant matter in a sample that is cheap, light in weight and small in size.
Yet another object of the invention is to provide an apparatus that for beneficial manufacturing and service purposes comprises no moving parts at all.
The objects mentioned above are achieved according to the invention by a method, an apparatus, and a combination of an apparatus and a sample device having the features defined in the appended claims.
According to a first aspect of the present invention there is disclosed an apparatus for measuring low energy sample radiation emanating from a sample containing a radiant matter, comprising
first and second radiation detectors for measuring said radiation and background radiation, said first and second detectors being positioned substantially parallel with their respective active surfaces facing each other in an aligned position, at a distance allowing for temporary insertion of a sample device of planar configuration in a measurement cavity between the detectors;
external shielding means enclosing the radiation detectors, said shielding means reducing background radiation present in the measurement cavity, said shielding means being provided with an opening for receiving said sample device;
electronic processing means for handling decay pulses received from the radiation detectors, calculating from said pulses the radiation originating from the sample and evaluating the result of said calculation; and
means for recording and/or displaying the results of said evaluation.
According to a second aspect of the present invention there is disclosed a combination of an apparatus described above and a sample device having a planar configuration and comprising a sample carrier and radiant sample matter carried by said sample carrier, said radiant sample matter being provided on said sample carrier such that sample radiation radiates from both surface sides of said sample carrier, said surface sides facing said first and second radiation detectors, when the sample device has been inserted into said apparatus.
According to a third aspect of the present invention there is disclosed a combination of an apparatus described above and a sample device having a planar configuration and comprising a sample carrier and radiant sample matter carried by said sample carrier, said radiant sample matter being provided on said sample carrier such that sample radiation substantially only radiates from one surface side of said sample carrier, said one surface side facing said first radiation detector when the sample device has been inserted into said apparatus.
According to a fourth aspect of the present invention there is disclosed a method for measuring low energy sample radiation emanating from a sample containing a radiant matter, comprising the steps of:
inserting a sample into a measurement cavity, between two aligned radiation detectors facing each other, such that said sample radiation reaches only a first detector of said radiation detectors;
measuring, for a predetermined time period, the respective number of output pulses originating from ionising events occurring in the respective radiation detectors;
providing a first radiation value obtained from the number of pulses from said first detector, and a second radiation value obtained from the number of pulses from the second detector;
providing a sample radiation value by subtracting a background radiation value from said first value, wherein said background radiation value is based upon a historical background radiation value obtained prior to insertion of the sample, by means of said second detector, as well as said second radiation value;
evaluating said sample radiation value, thereby determining the amount of radiant matter in the sample.
According to a fifth aspect of the present invention there is disclosed a method for measuring low energy sample radiation emanating from a sample containing a radiant matter, comprising the steps of
inserting a sample into a measurement cavity, between two aligned radiation detectors facing each other;
measuring, for a predetermined time period, the respective number of output pulses originating from ionising events occurring in the respective radiation detectors;
providing a first radiation value obtained from the measured number of pulses from said first detector, and a second radiation value obtained from the measured number of pulses from the second detector;
providing a sample radiation value by subtracting a background radiation value from the sum of said first and second radiation values, wherein said background radiation value is based upon a historical background radiation value obtained prior to insertion of the sample; and
evaluating said sample radiation value, thereby determining the amount of radiant matter in the sample.
According to a sixth aspect of the present invention there is disclosed a method for measuring low energy sample radiation emanating from a sample containing a radiant matter, the method comprising
providing a first radiation detector and a second radiation detector such that the two radiation detectors both measure substantially the same background radiation;
using said second radiation detector for measuring a historical background radiation mean value;
thereafter positioning the sample relative to said radiation detectors such that sample radiation reaches said first radiation detector only;
measuring both output pulses from said first radiation detector and output pulses from said second radiation detector; and
calculating a sample radiation value by subtracting from a measured number of output pulses from said first radiation detector a corresponding background radiation value based upon said historical background radiation mean value and the measured number of output pulses from said second radiation detector.
According to a seventh aspect of the present invention there is disclosed A method for measuring low energy sample radiation emanating from a sample containing a radiant matter, the method comprising
providing a first radiation detector and a second radiation detector such that the two radiation detectors both measure substantially the same background radiation;
using said radiation detectors for measuring a historical background radiation mean value;
thereafter positioning the sample relative to said radiation detectors such that sample radiation reaches both radiation detectors;
measuring both output pulses from said first radiation detector and output pulses from said second radiation detector; and
calculating a sample radiation value by subtracting from a measured number of output pulses from said detectors a corresponding background radiation value based upon said historical background radiation mean value.
Thus, the first and second radiation detectors are positioned in the measurement cavity substantially parallel in an aligned position, with their respective active surfaces facing each other. The detectors are adapted for enabling them to measure radiation emanating from a sample device, of substantially planar configuration, inserted into the measuring cavity, the sample being positioned as close as possible and substantially parallel to the detectors, so that scattering is minimised and essentially all radiation emanating from the sample will be able to reach the detectors. This configuration, in which the detectors face each other with the sample device inserted there between, ensures that no shielding from the sample radiation by the other detector will take place.
Said first and second radiation detectors can both be used for measuring sample radiation. This enables detection of radiation emanating from radiating surfaces on both sides of the planar configured sample device, and increases the number of ionising events measured. Thus, a higher diagnostic accuracy can be achieved. In this case, the background radiation to be subtracted from the sample measurement results constitutes a historical background radiation value, said historical value being obtained and updated prior to each insertion of a sample device into the measurement cavity. The historical value can be obtained using both radiation detectors for measuring the background radiation.
Alternatively, the second radiation detector can be used for measuring background radiation only. This provides a lower count of ionising events, but instead it gives a higher accuracy regarding the measured amount of background radiation to be subtracted, due to the fact that the amount of background radiation present in the measurement cavity changes over time. However, it has surprisingly been found that when subtracting the background radiation from the measurements of sample radiation a considerable improvement of the measurement accuracy can be achieved if the value corresponding to background radiation is a weighted mean value calculated from the result of the background radiation measurements performed during the sample radiation measurements and a historical background radiation value, said historical value being obtained and updated prior to each insertion of a sample device into the measurement cavity.
In order to ensure that sample radiation is not detected by the second radiation detector, in the case that the second detector is arranged to measure background radiation only, there can be provided internal shielding means. Said shielding means can either be a part of the apparatus, a part of the sample device or both. Preferably the sample radiation shield is removably mounted (inherently if in the sample device) so that it can be easily replaced if contaminated. In order to obtain a reliable value of the amount of background radiation present in the measuring cavity, it is important that the internal shielding of the second detector efficiently prevents radiation from the sample to reach the second detector, while at the same time preventing as little background radiation as possible from reaching the second detector. Therefore, the material and thickness of the internal shielding has to be chosen with respect to the energy content and type of the sample radiation being measured.
In order to further improve the accuracy regarding the measuring of background radiation present in the measurement cavity during the sample radiation measurements, in the case of both the first and second detector measuring sample radiation, a third radiation detector can be provided within the measurement cavity. This enables measuring of background radiation simultaneously with the measuring of sample radiation. Said third detector can be placed behind said first or second detector, seen from the sample device, or in a position as close as possible to the sample.
When measuring the sample radiation or the background radiation coincidental pulses, i.e. radiation pulses that strikes both the first and second radiation detectors simultaneously, can automatically be disregarded, since coincidental pulses can, with a very high probability, not originate from the sample due to the orientation of the radiating surfaces of the sample relative the first and second radiation detectors and to the relative small number of ionising events emanating from the sample. This can be done by not, or separately, registering ionising events occurring in both the first and second radiation detectors within a predetermined, short time interval.
Preferably, the apparatus according to the invention further comprises a sample position detector for detecting whether the sample is in its correct position and to prevent the start of a sample radiation measurement if this is not the case. Said detector is used in order to ensure that as much of the sample radiation as possible is caught by the first radiation detector. If the sample would not be in the correct position, scattering of the radiation would result in a false, low, count of ionising events and a false value of the amount of radiant matter. When the apparatus is used for diagnostic purposes this in turn could lead to a wrong diagnosis.
In order to decrease the amount of background radiation present in the measuring cavity, said cavity can be enclosed by an external shield made out of a high density material. This will improve the signal to noise ratio and thereby increase the accuracy of the measurements.
In order for the sample not to contaminate the measuring cavity, the sample device can be provided with a sample matter cover that is not permeable to the sample matter but is permeable to the sample radiation. Such a cover can consist of a thin film of some sort. Preferably, the cover consists of a mylar film with a typical thickness of about 1 xcexcm.
The radiation detectors will in the following description be illustrated in a horizontal position. However, this shall not be seen as a restriction of the invention, merely as an illustration of preferred embodiments of the present invention. Several other alternatives are contemplated within the scope of the invention, such as placing the detectors vertically, etc. Placing the first and second detectors vertically, with the sample device placed vertically between the detectors, would eliminate the risk of the sample matter contaminating these detectors because the radiating matter can not fall on to the detectors.
With regard to means used for the actual detection of radiation, the man skilled in the art realises that various types of detector means could be used, such as proportional counters or, as is preferred, Geiger-Mxc3xcller tubes. Thus, for the purpose of making the description more comprehensive, the rest of the description will refer to Geiger-Mxc3xcller tubes as means for detecting radiation.
The radiation detectors in the apparatus according to the invention are not limited to a specific shape or size. However, since it is an object of the present invention to provide a cheap and small measuring apparatus the Geiger-Mxc3xcller tubes shall consequently meet the same requirements. The described configuration of the apparatus along with the described method of measuring sample radiation enables, with maintained satisfactory diagnostic accuracy, the use of the cheapest and smallest Geiger-Mxc3xcller tubes in use today.